The present invention relates to microcolumns for extraction of an analyte from a liquid sample, and particularly extraction of an analyte from biological fluids.
Accurate and inexpensive detection of analytes present in liquid samples, for example in biological fluids, such as blood and urine, is important to health care. Tests for analytes in blood and urine are conducted to monitor the health of patients, detect the presence of disease conditions, and monitor for the use of illegal or restricted drugs. For example, doctors, when administering drugs such as antiarrythymics, asthmatic drugs, insulin, and anticoagulants, check the drug content of the blood to regulate the dosages of the patient. Drugs that can be abused, such as heroin, marijuana, cocaine, and codeine, can be tested to determine abuse of the drug, such as by employees and by athletes.
A technique used for detection of analytes includes selectively extracting the analyte from the biological fluid onto a solid media. The analyte is then removed from the solid media by a suitable elution liquid, and tests are conducted to determine whether the analyte is present in the eluent liquid, such as by gas or liquid chromatography.
Prior art extraction columns have been effectively used. For example, it is known to use particulate silica as the solid media in a column. In addition, silica has been provided embedded within an inert matrix of polytetrafluoroethylene ("PTFE") in the form of an extraction disk, which can be preloaded in a plastic barrel.
A problem with use of PTPE to hold the silica is that PTFE is hydrophobic and can require preconditioning with alcohol and high pressure so that the aqueous sample can flow therethrough. This increases the time and manpower required for the analysis.
Although these prior art devices can be effective, it is desirable to improve on these devices. It is desirable that the extraction device be fast, remove a high percentage of the analyte from the sample, be transportable, storable without damage, and be inexpensive. Moreover, it is desirable that any such device be compatible with existing automated equipment, and not leach into the biological fluid or the eluent liquid, any compound that could interfere with the analytical results.
Moreover, it is desirable to minimize the volume of biological fluid and wash eluent liquid. By minimizing the liquid volume, a more concentrated sample is obtained for analysis, the sensitivity of the test is enhanced, and less biological fluid needs to be obtained from the subject. High yields from the biological fluid with minimum elution volumes can be obtained by maintaining uniform flow through the extraction media, with no channeling and no dead volume.